Filter screen assembly

ABSTRACT

A fine filter screen assembly includes a frame assembly and a rotatable shaft supported in the frame. A drive is configured to controllably rotate the shaft and at least one drive drum is positioned on the shaft for rotation therewith. The drive drum has an external surface that is substantially defined by a high friction surface and a fine filter grid is supported in the frame assembly and positioned about and in contact with the drive drum such that rotation of the shaft causes rotation of the fine filter grid.

RELATED APPLICATION DATA

This is a divisional patent application of U.S. patent application Ser.No. 10/364,747 filed on Feb. 10, 2003 now U.S. Pat. No. 6,942,789, whichclaims benefit under 35 U.S.C. Section 119(e) of U.S. ProvisionalApplication No. 60/355,003 filed Feb. 8, 2002, both of which are fullyincorporated herein by reference.

BACKGROUND

Difficulties are encountered in practice in the treatment ofcontaminated water flows such as sewage prior to fine filtration, due tothe presence of heavy and generally untreatable objects such as rags,string, plastic bags, and the like. Wastewater treatment plantstypically utilize some type of screening equipment to remove harmfuldebris contained in the waste stream flow. Screening equipment is oftenutilized in the headworks section of the plant, and is the first area tocome in contact with the waste stream. The screens are typically madefrom corrosion resistant materials such as 304 or 316 stainless steel,plastics or other synthetic materials. In order to protect thedownstream equipment and processes, screening equipment is designed andincorporated in a plant to remove a large majority of debris before itcomes into contact with any downstream equipment. If such items are notremoved, proper and adequate treatment of the liquid does not result,and blockage of ducts and channels may occur.

There are many different screening equipment designs. A screening deviceis known comprising a continuously movable endless conveyor loop formedof a series of interconnected link pieces each having a lifting hook onwhich material to be screened is collected during movement through thecontaminated water flow. Fine screens of this nature are typicallydefined by the size of the screen openings, which can be from as smallas a quarter inch to one-half inch. These units can also be sized tohave clear openings as large as 2 inches or more, but typically are not.The screen openings are designed to address both the horizontal andvertical limiting dimensions. The horizontal dimension is the smalldimension and definition of the continuous belt, for example,one-quarter inch. The vertical dimension is typically significantlylarger (approx. 4 in. or 6 in.) and is tied to the length of individualelements and the interconnected driving links and support shafts orpivot rods.

Another type of screening device is a panel type filter screen assembly.The panel type filter screen units generally include a plurality offilter panels and an endless chain operationally connected to the filterpanels to move the filter panels through the water or wastewater whilefollowing a guided path in the structural frame of the filter screen.Typical panel type filter screen units utilize a plurality of filterpanels that are fabricated of metal such as steel or stainless steel orother non-corrosive material. Such a panel typically consists of a largenumber of metal bars 2 spaced from and generally parallel to one anotherand welded vertically to a metal panel frame 4. The filter panelassemblies are operationally attached to the drive system, such as to anendless chain, and movement of the chain in turn moves the filter panelassemblies along a guided path within the structural frame of the screenfilter apparatus 10.

An illustrative screen filter apparatus 10 is shown in FIGS. 1–3.Referring first to FIG. 1, it will there be seen that a waste materialfiltering apparatus 10 of the prior art generally includes a frame 11, aplurality of pipe spreaders 13, a drive motor 15 connected to a drivesprocket assembly 22 by a drive belt or chain 23, shown in phantomlines, and a rotating screen assembly 17 driven by the sprocketassembly. Referring to FIG. 2, the apparatus 10 sits in a channel 21within which flows a stream of water containing solid waste.

The rotating grid assembly 17 is a link type grid that includes aplurality of vertically disposed, laterally spaced apart link members 12that are disposed in articulated relation to one another. The trailingend of each link 12 has an integral horizontally-extending part 16 thathelps hold and lift solid matter from the stream as the screen segmentstravel upwardly on the upstream side of the machine. Means are providedat the discharge end of the apparatus for dumping the matter so liftedinto a solid waste collection container.

The opposite ends of each link 12 is mounted on a shaft 31, 33. Thetrailing end of each link 12 is the aforementionedhorizontally-extending member 16 that helps hold and lift solid matterfrom the water stream as the links rotate, as is perhaps best understoodby observing the links at the lower left corner of FIG. 1. The uppermostor leading end of each link is denoted 18. Plural directional arrows,collectively denoted 19, show the path of travel followed by the linksas the machine operates. The orientation of machine 10 in a channel ofwater is shown in FIG. 2. The concrete channel is denoted 21. In thisparticular example, there are about twenty five upstanding screensegments disposed in equidistantly spaced lateral relation to oneanother, each screen segment being formed by a group of articulated linkmembers 12.

The conventional assembly pattern of links is best understood inconnection with FIG. 3. The links 12 of the prior art rotating screenare typically assembled in the following pattern. The trailing andleading ends 16, 18, respectively, of a link 12 a are slipped onto apair of contiguous shafts 31, 33, with the same procedure repeated aboutthe remaining alternating shafts 31, 33 of the screen assembly 17. Thetrailing end of the next link 12 b is then slid onto shaft 31 and theleading end of that link is slid onto shaft 33. The alternating patternis then followed as links are placed on all of the shafts 31, 33.Spacers 20 are then added to each shaft, and the same pattern ofassembly is repeated to construct a screen assembly 17 of a desiredwidth. The alternating nature of the links 12 a, 12 b connects the linksinto a continuous loop.

The rotating grid assembly 17 is generally a large structure that isdirectly driven by the sprocket drive assembly 22 and is undersignificant tension. The sprocket assembly 22 generally includes aplurality of laterally spaced apart motor-driven sprocket segments. Thesprocket segments are positioned in offset relation to the individuallinks 12 so that as the links 12 pass there over, the sprocket segmentsenter into the spaces between the links 12. Such a sprocket driveassembly 22 is subject to jamming because the apparatus performs wellonly when the sprocket segments are perfectly or almost perfectlyaligned with respect to each contiguous set of links. In order toestablish such perfect alignment, the spacers between the sprockets mustbe manufactured to very tight tolerances. However, a single drive shaftmay include from 10 to 150 or more spacers. Any inaccuracy in theindividual spacer tolerances is accumulated across the shaft to create atotal inaccuracy that is often unacceptable. Even when the sprocketsegments and links 12 are in their respective ideal relative positions,the sprocket segments rub against their contiguous links 12 inalternating succession, displacing each link about one-sixteenth of aninch per rub. More particularly, the links are displaced in a firstdirection in a first rub, and are displaced in an opposite directionduring a second rub. Due to the rubbing and alternating displacement ofthe links, the sprocket segments and links 12 eventually becomemisaligned and collide with one another. This bends the links 12,damages the sprocket segments, and prevents further rotation of therotating screens until the apparatus has been disassembled and new links12 and sprocket segments installed. The repair procedure typicallyrequires the grid assembly to be dismantled to expose the drive shaftand sprockets for repair or the entire assembly must be removed andreturned to a shop for repair.

To define the path of the screen assembly 17, the prior art systemincludes sliding wear bars 40 to define the path of the screen loopadjacent the top of the filter assembly 10 and inner and outer guiderails 42, 44 and a bottom guide 46 are provided adjacent the bottom ofthe assembly 10 to track the screen assembly 17. The wear bars 40 aresubject to significant wear from the continuous travel of the links 12there over. The internal positioning of the wear bars 40 make themdifficult to maintain and replace. Additionally, the wear bars 40 causewear and additional frictional load on the screen assembly 17. The guiderails 42, 44 and bottom guide 46 are also subject to wear. Additionally,since these components 42–46 are in the fluid stream, they act as apoint of debris build-up. The built up debris negatively effects flowthroughput. Additionally, grit, sand and the like trapped between theguides 42, 44 and 46 and the screen assembly 17 acts to accelerate wearon the screen assembly 17. The limited accessibility makes componentreplacement and debris flushing difficult.

SUMMARY

The present invention provides a waste water filter assembly that has asubstantially open foot section to promote efficient flow through. Thefilter screen is generally free hanging with spaced apart guide railsand a wear bar defining the filter path extents, but not confining thefilter screen grid. The present invention further provides a driveassembly with square, high friction drive drums mounted on a driveshaft. Each side of the drum is provided with a high friction material,for example, high friction brake pad lining. The present inventionfurther provides idler roller assemblies mounted for guiding the filterscreen adjacent the filter assembly head. Each roller preferablyincludes replaceable split roller wheels with non-lubricated bushingsthat align with and contact respective guide link sections on the screenloop. Each roller is preferably free-wheeling and independent of theother roller wheels of the assembly. The rollers are preferably sizedslightly larger toward the outer edges of the screen to maintain propertracking of the screen loop. The open foot assembly, drive assembly andidler roller assembly are useable with filter grids of both the linkelement type and the panel type.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a prior art waste material filterassembly;

FIG. 2 is a front elevational view of the filter assembly of FIG. 1disposed in a channel for carrying waste water;

FIG. 3 is an exploded perspective view showing the assembly of the priorart filter assembly;

FIG. 4 is a side elevational view of a waste water filter assembly inaccordance with the present invention with the filter screen cleaninggrid omitted;

FIGS. 5 and 6 are partial elevational views of the filter assembly inaccordance with the present invention with the filter screen properlytensioned (FIG. 5) and in need of tensioning (FIG. 6);

FIG. 7 is a sectional view taken along the line 7—7 in FIG. 4;

FIG. 8 is a front elevational view taken along the line 8—8 in FIG. 4with one of the side plates removed;

FIG. 9 is a sectional view taken along the line 9—9 in FIG. 4;

FIG. 10 is a sectional view taken along the line 10—10 in FIG. 9;

FIG. 11 is a sectional view taken along the line 11—11 in FIG. 10;

FIG. 12 is a partial schematic illustration of the preferred headsection of the filter assembly in accordance with the present invention;

FIG. 13 is a sectional view taken along the line 13—13 in FIG. 12;

FIG. 14 is a side elevational view of the preferred drive shaft;

FIG. 15 is a front elevational view taken along the line 15—15 in FIG.13;

FIG. 16 is a schematic illustration of the filter screen rotating gridpositioned about the preferred drive drum assembly of the presentinvention;

FIG. 17 is a side elevational view, with half of the assembly insection, of a preferred idler roller assembly of the present invention;

FIG. 18 is a front elevational view of a preferred idler roller assemblyof the present invention;

FIG. 19 is a side elevational view of a preferred idler roller of thepresent invention;

FIG. 20 is a front elevational view of the idler roller wheel of FIG.19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described with reference to theaccompanying drawing figures wherein like numbers represent likeelements throughout. Certain terminology, for example, “top”, “bottom”,“right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and“rearward”, is used in the following description for relativedescriptive clarity only and is not intended to be limiting.

The preferred waste water filter screen assembly 100 of the presentinvention is shown in FIGS. 4–18. Referring to FIGS. 4 and 5, the filterscreen assembly 100 generally includes a frame assembly 110 in which afine filter rotating grid 130 (see FIG. 5) travels. The rotating grid130 may be a link type grid or a panel type grid. The rotating grid 130is driven by a drive assembly 190 adjacent the filter screen assemblyhead 180. Idler roller assemblies 220 are provided to guide the rotatinggrid 130 through the filter screen assembly head 180. Water travels inthe direction of the arrow A in FIG. 4 and passes through the rotatinggrid 130 in the foot section 140 of the filter screen assembly 100.

The preferred embodiment of the foot section 140 is shown in FIGS. 4–11.The foot section 140 includes an open area 142 through which the watertravels. The open area 142 is defined by thin side walls 144 and 146 anda bottom plate 148. Removable side plates 150 and seal members 152 sealthe side walls 144 and 146 to the water channel. However, removal of theside plates 150 and seal members 152 allows easy access to the internalcomponents. The rotating grid 130 travels between spaced apart inner andouter guide members. In the preferred embodiment, the guide members aredefined by outer guide rails 160 and an inner semi-circular wear bar166. The guide rails 160 defining the outer extent of the grid 130travel path and the inner wear bar 166 defining the inner extent of thegrid 130 travel path.

The rotating grid 130 does not ride on the guide rails 160 and the innerwear bar 166. Instead, the guide rails 160 and wear bar 166 only definethe extents of the rotating grid path, with the rotating grid 130preferably hanging substantially freely between the guide rails 160 andbar 166 as shown in FIG. 5. The rotating grid 130 has a thickness T andthe guide rails 160 and bar 166 are spaced a distance D that issubstantially greater than the thickness T. The distance D is preferablyapproximately twice the thickness T. As such, in operation the grid 130is generally not in contact with the guide rails 160, as shown in FIG.5. In the event the rotating grid 130 sags, stretches or is otherwisemisaligned, see FIG. 6, the grid 130 is be supported by the guide rails160 until the grid 130 is repositioned to the desired operatingposition. The filter screen assembly 100 preferably includes anadjustment mechanism 154 that allows the grid 130 to be lifted to thedesired operating position. As can be seen from the figures, the footsection 140 is free of side guide rails that define a specific traveltrack for the rotating grid 130.

Referring to FIGS. 9–11, the guide rails 160 are preferably positionedat spaced apart locations that are to align with guide portions of therotating grid 130. Each guide rail 160 includes an arcuate planarsurface 162 supported on a support member 164 extending between thebottom plate 148 and a rear support bar 165. The planar surfaces 162 arepreferably manufactured from stainless steel and are removable to alloweasy maintenance and replacement. Water and grit are free to passthrough the open area 142 and do not get caught between the grid 130 andthe guide rails 160. The relatively small cross-sectional area and thespacing of the guide rails 160 allows grit and smaller debris to easilytravel past the rails 160 without any build-up. An adjustable dualinfluent brush 168 is positioned along the bottom plate 148 to preventlarger debris from passing past the grid 130. Larger debris contacts thebrush 168 and is directed upward where it is picked up and removed bythe grid 130. The brush 168 is right within the open area 142 so it iseasily accessible, cleanable and replaceable.

The preferred drive shaft assembly 190 of the present invention is shownin FIGS. 12–16. The drive shaft assembly 190 includes a drive shaft 192driven by a motor (not shown) or the like. The shaft 192 is mounted inan external bearing assembly 194 that allows for easy removal of thedrive shaft 192. As seen in FIG. 14, the shaft 192 preferably has endkey slots 193 for engaging the shaft 192 with he bearing assembly 194and a center key slot 195. A plurality of drive drums 196 are mounted onthe shaft 192. Each drum 196 has a square frame 198 mounted on the driveshaft 192, via set screws 197 received in the center key slot 195, forrotation therewith. Each side of the frame 198 is provided with a highfriction material pad 200, for example, high friction brake pad lining.The drums pads 200 preferably have a contact length approximately equalto the distance between adjacent screen guide links (not shown) suchthat the high friction pad 200 contacts almost all of the filterelements 12 in that grid section. The weight of the rotating grid 130allows the friction between the drum pads 200 and the filter elements 12to drive the rotating grid 130. Any misalignment between the filterelements 12 is absorbed by the friction pads 200 such that proper grid130 driving is maintained even if the filter elements 12 are misaligned.

Referring to FIGS. 12 and 17, a preferred embodiment of the idler rollerassembly 220 is shown. The idler roller assembly 220 comprises a shaft222 mounted between a pair of roller support members 240. Theillustrated shaft 222 has a center roller 228 and a pair of end rollers230. Each roller wheel 228, 230 aligns with and contacts a respectiveguide link (not shown) on the rotating grid 130. The number andpositioning of the rollers 228, 230 can be adjusted to meet therequirements of a given filter screen assembly 100. Each roller 228, 230is a solid cylinder with a center hole for positioning on the shaft 222.The rollers 228, 230 may be press fit, keyed, welded or otherwisesecured to the shaft 222. The rollers 228, 230 are preferably sized suchthat the outer rollers 230 are slightly larger to maintain propertracking of the rotating grid 130, but may have various configurations.

The shaft 222 is a hollow tube with a smooth surface roll sleeve 230press fit in each end thereof. Set holes 224 extend through the shaft222 and sleeves 226 at each end of the shaft 222. The roll sleeves 226are configured to receive and rotate with a support shaft 242 extendingfrom each support member 240. Each support shaft 242 has set bores 243configured to align with the set holes 224 such that set screws (notshown) journal the shaft 222 to the support shafts 242. Each supportshaft 242 extends through a hole 147 in a respective side wall 144, 146of the filter screen assembly 100. The support shaft 242 is received ina bushing 246 that allows smooth rotation of the support shaft 242. Thebushing 246 is preferably manufactured from a synthetic material, forexample, Acetron GP. The bushing 246 is supported in a sleeve 248secured between a mounting plate 244 and an end cap 250. The shaft 222can easily be removed for maintenance or replacement by simply releasingthe set screws and removing the support assemblies 240 which areexternal and easily removed.

An alternate embodiment of the idler roller assembly 220′ is shown inFIGS. 18–20. The roller assembly 220′ includes a shaft 322 mounted inexternal roller bearings 324 that allow rotating of the shaft 322 ifnecessary and for easy removal of the idler roller assembly 220′. Aplurality of roller supports 326 are mounted on the shaft 322 forsupport of roller wheels 328. Each roller wheel 328 preferably includesa replaceable split steel roller wheel 334 with an internal non-metallicbushing 336. Each roller wheel 328 aligns with and contacts a respectiveguide link (not shown) on the rotating grid 130. The roller wheels 328are preferably secured between opposed plates 330, 332 to create aconfined path for the roller wheel 328 and to add rigidity. The rollerwheels 328 are preferably sized such that the outer roller wheels 328′are slightly larger to maintain proper tracking of the rotating grid130. The idler nature of the independent roller wheels 328 of the rollerassembly 220 significantly reduces the frictional load on the rotatinggrid 130 and allows each guide link grid path to act independently ofone another regardless of accumulated tolerances throughout the grid.

1. A fine filter screen assembly comprising: a frame assembly; arotatable shaft supported in the frame; a drive configured tocontrollably rotate the shaft; at least one drive drum positioned on theshaft for rotation therewith; the drive drum has an external surfacethat is substantially defined by a high friction surface; and a finefilter grid supported in the frame assembly and positioned about and incontact with the drive drum such that rotation of the shaft causesrotation of the fine filter grid, wherein the drum has a plurality ofrectangular sides with each side having a rectangular high friction pad,with a given height h and length 1, attached thereto.
 2. The fine filterscreen assembly of claim 1 wherein the filter grid comprises a pluralityof grid sections, each grid section having a given height H and length Land each friction pad has a height h substantially equal to the gridsection height H.
 3. The fine filter screen assembly of claim 1 whereinthe filter grid comprises a plurality of grid sections, each gridsection having a given height H and length L and each friction pad has alength 1 substantially equal to the grid section length L.
 4. The finefilter assembly of claim 1 wherein the high friction surface includeshigh friction brake pad lining.
 5. The fine filter assembly of claim 1,wherein the filter grid comprises a plurality of grid sectionsinterconnected by a plurality of shafts, and wherein the drive drumengages the grid sections.
 6. The fine filter assembly of claim 5,wherein the drive drum does not directly engage the shafts.
 7. A filterscreen assembly comprising: a frame assembly; a grid supported in theframe assembly and rotatable within the frame assembly; and a drive drumengaged with the grid such that rotation of the drive drum produces acorresponding rotation of the grid, the drive drum including a pluralityof substantially planar sides that are engageable with the grid and aplurality of high friction pads, each high friction pad attached to oneof the substantially planar sides.
 8. The filter screen assembly ofclaim 7, further comprising a shaft supported for rotation, the drivedrum fixedly attached to the shaft.
 9. The filter screen assembly ofclaim 8, further comprising a second drive drum fixedly attached to theshaft and defining a second plurality of substantially planar sides thatare engageable with the grid.
 10. The filter screen assembly of claim 8,wherein the shaft is supported for rotation by the frame.
 11. The filterscreen assembly of claim 7, further comprising a drive configured tocontrollably rotate the drive drum.
 12. The filter screen assembly ofclaim 7, wherein each of the high-friction pads defines a substantiallyplanar engagement surface sized to engage the grid.
 13. The filterscreen assembly of claim 7, wherein the grid comprises a plurality ofgrid sections interconnected by a plurality of shafts, and wherein thedrive drum engages the grid sections.
 14. The filter screen assembly ofclaim 7, wherein the sole engagement between the drive drum and the gridis frictional.
 15. A filter screen assembly comprising: a frameassembly; a shaft supported for rotation by the frame assembly; aplurality of grid sections interconnected to define a grid assembly, thegrid assembly supported for movement by the frame assembly; and a drivedrum coupled to the shaft and including a plurality of substantiallyplanar sides and a plurality of high friction pads, each high frictionpad attached to one of the substantially planar sides, each of theplanar sides sized to independently frictionally engage one of theplurality of grid sections such that rotation of the shaft produces acorresponding rotation of the drive drum and movement of the gridassembly.
 16. The filter screen assembly of claim 15, further comprisinga drive configured to controllably rotate the shaft.
 17. The filterscreen assembly of claim 15, wherein each of the high-friction padsincludes a substantially planar engagement surface sized to engage oneof the grid sections.
 18. The filter screen assembly of claim 15,further comprising a second drive drum fixedly attached to the shaft anddefining a second plurality of substantially planar sides that are sizedto independently frictionally engage one of the plurality of gridsections.